The present invention relates to a pencil sharpener including a blade, more particularly to a pencil sharpener which has a simple structure and which can sharpen a soft wood and a hard lead of a pencil simultaneously in a pointed and fine state by the use of a plate blade.
With regard to a conventional pencil sharpener in which a plate blade is employed, as shown in FIGS. 1 to 3, a body 1 of the sharpener is provided with a conical pencil-insertion bore 2 having a suitable taper angle to an axis of a pencil to be sharpened and a blade-bearing surface 3 having a suitable width disposed along the bore 2, and one plate blade 4 is secured on the surface 3 by means of a screw. In this constitution of the sharpener, however, when used, the blade 4 bites into a wood and a lead of the pencil, which are different in hardness, at the same depth. Therefore, the wood portion near to the lead tends to be ripped off the pencil and the lead tends to be broken, further a sharpened surface of the pencil is liable to be rough, and it is thus very difficult to sharpen the pencil in a finely pointed state by the conventional one. This is evidenced by the fact that there is sold a new sharpener having two pencil-insertion bores which are each provided with a blade and which are different in taper of each blade, one bore serving to sharpen a wood only; another bore serving to sharpen a lead only (manufactured by KUM in West Germany, trade name: Automatic 2).
Further, in the conventional pencil sharpener, the blade is secured to the body of the sharpener by means of a screw or the like. Therefore, the angle of the blade with respect to the bore cannot be adjusted. As improved types, there are suggested the structure that a prolonged orifice is provided along a longitudinal direction of a blade and the blade is fixed by a screw slidably in a forward and a backward directions (Japanese Utility Model Publication No. 29598/1980) and the structure that a knob having a spirally upward guide surface on the rear side of a sharpener body is disposed so that the whole of a blade may be moved upward and downward (Japanese Utility Model Publication No. 46554/1980). In each of these devices, however, the blade is supported at an angle approximately equal to the taper angle of a pencil-insertion bore and still bites into a wood and a lead of a pencil at the same depth. Therefore, they cannot eliminate the above-mentioned drawbacks that the wood and the lead of the pencil are difficult to be simultaneously sharpened in a fine state by one blade, though they permit sharpening pencils having a variety of sizes.
Functions required for a pencil sharpener are (1) being able to sharpen a pencil smoothly and finely, (2) being able to sharpen a lead of the pencil to a desired thickness, (3) being able to prevent over-sharpening of the pencil, and (4) being able to sharpen the pencil in a fine and pointed state. However, none of conventional pencil sharpeners have these functions at all.
For example, the pencil sharpeners mentioned above and shown in FIGS. 1 to 3 do not have the preceding functions 1 to 4. Further, the pencil sharpeners described in Japanese Utility Model Nos. 29598/1980 and 46554/1980 do not have the functions 1, 3 and 4 above, and cannot carry out a fine adjustment of the thickness of a lead with regard to the function 2 above, though being able to make a rough adjustment thereof.
Lately, there has been disclosed an electric pencil sharpener in which a blade is fixed at such an angle as the edge of the blade bite more into a conical bore of the sharpener on the rear side thereof (Japanese Utility Model Provisional Publication No. 81095/1980). However, this pencil sharpener can sharpen a pencil finely but has no functions 2 and 3 mentioned above.
FIG. 4 schematically exhibits a typical structure of a pencil sharpener having a spiral cutter. In the drawing, reference numeral 11 is a body of the pencil sharpener, numeral 12 is a pencil-insertion bore, 14 is a blade (which rotates in an arrow direction in the drawing), 16 is a stopper and symbol P is a pencil. When the sharpener is used, the pencil hits against the stopper at the tip of the lead. That is to say, the pencil can be sharpened to a desired thickness of the lead by moving it in a right and a left directions shown by an arrow symbol in the drawing.
In this structure, over-sharpening can be prevented by the engagement of the tip of the lead of the pencil P with the stopper 16, but on the contrary, the tip of the lead cannot be brought into contact with the blade and thus cannot be pointedly sharpened. Further, the fixation of the stopper 16 makes the structure of the pencil sharpener complicated and also makes the pencil sharpener itself expensive.
As understood from the above, none of the conventional pencil sharpeners have the four functions at all, and if it is attempted that all of them are satisfied, the structure of the pencil sharpener will be very intricate, which will require much labor for the manufacture, and the sharpener itself will be expensive.